The invention relates to an apparatus for testing an electric motor to detect the presence of motion without a need for the addition of mechanical components to the motor.
The widespread use of electric motors in various types of machinery and equipment has led to a need for a simple and reliable means for determining and indicating to an operator whether or not the motor is in motion. This need is readily apparent in the field of motor-driven machinery which is of a size such that the inertia of the motor and, the various machine elements causes the motor to continue to rotate, or coast, for a time after the motor power has been disconnected. An operator of such a machine, after shutting off the power to the motor, often tends to forget about or to disregard these inertia effects and thinking that the machine is at rest, may place his hands or a portion of his body in a location which can result in an accident. Because of the critical relationship of the motion of the electrical motor and the machine to the safety of the operator, a desirable motion detector, in addition to being inherently highly reliable, must also have failure modes which result in an indication that there is motion of the motor even when in fact the motor is stationary. In addition, a desirable motion detector, in order to gain acceptance as a safety device, must be relatively simple to install and must not impede the normal operation of the motor. This requirement, in connection with the requirement for high reliability, rules out the use of conventional mechanical components such as revolution counters and the like.